The present invention concerns an intake air control device for an internal combustion engine, which has a surge tank for temporarily storing the intake air taken in through the throttle valve linked in motion with the accelerator pedal, and a low speed and a high speed intake tube for supplying the intake air from the surge tank to the combustion chamber.
When operating the internal combustion engine at a low load before or after warming up including idling, poor combustion generally occurs due to the low flowing speed of the intake air compared to the engine operation at a high speed. In order to overcome this problem, there has been proposed a high performance engine in which each of the cylinders is provided with a long low speed intake passage for receiving the fresh air to improve the efficiency of filling the cylinder with the fresh air at a low speed and a short high speed intake passage for quickly receiving the fresh air to reduce the flowing resistance of the intake air at a high speed.
In such conventional intake control, the high speed intake passage is completely closed at a low speed, which results in an irregular engine operation due to the abrupt change of the amount of the intake air, and additionally makes it impossible to utilize the inertia of the intake thus reducing the filling efficiency of the intake air.